1. Field of the Invention
The present invention relates to a process for removing acidic gases such as H.sub.2 S, COS, CO.sub.2 and HCN from mixtures of lower boiling hydrocarbons.
2. Description of the Prior Art
Mixtures of light hydrocarbons, such as mixtures commonly known as light ends, which usually result from the thermal decomposition of high temperature petroleum refining operations are often recovered and separated into two or more hydrocarbon streams in a light ends treating operation, such as deethanizer and debutanizer towers. The acidic gases contained in these light ends cause corrosion of the light ends treating equipment.
Prior art technology typically consisted of compressing the gas portion and pumping the liquid portion of these light hydrocarbons and feeding them to a light ends fractionation system. Any acidic gases contained in the light ends were carried through the light ends fractionation towers and eventually removed from the separated products. In a typical light ends sequence, consisting of an absorber deethanizer tower followed by a dubutanizer, a portion of the acid gases would go to the overhead product from the deethanizer and be scrubbed out by a downstream scrubber using an amine solution or other absorbent. The remainder of the acid gases would typically concentrate on the overhead product of the debutanizer, usually a C.sub.3 /C.sub.4 LPG stream, and be removed by liquid/liquid treating with an amine and/or caustic solution.
The presence of corrosive agents in the light ends towers in such schemes as described above has been known to cause severe corrosion of the fractionating vessels and associated equipment. Also, the presence of HCN, which reacts irreversibly with the amine to form degradation products, has resulted in large amine losses.
The present invention provides a process which relieves both of these conditions by (1) placing the acid gas removal system upstream of the light ends towers and (2) placing a water scrubber to remove the bulk of the HCN upstream of the amine tower.
A method has now been found whereby the acidic gases are removed from the light ends prior to processing the light ends in light ends recovery equipment.